Abstract

On page 449 of this issue1, Pereverzev et al. report mechanical oscillations spontaneously generated by two weakly coupled volumes of superfluid 3He - providing a direct demonstration of its large scale quantum behaviour. At very low temperatures all materials tend to fall into highly ordered states. Most commonly, this order takes the form of perfect crystals, but there are exceptions. Most strikingly, the two isotopes of helium (3He and 4He) never solidify at all under their vapour pressures. Rather, they stay liquid to the lowest temperatures attainable, and are assumed to remain so right down to absolute zero.